Mr.Steamer Commercial Steambath CU750A temp is to high it is out of control

There are only 3 likely causes. The first and most likely is the room sensor inside the shower. This is a resistive type sensor that communicates the temperature in the room to the controller via ohm ratings. There is an equivalent ohm rating for every degree of temperature it correlates to and that is how the temperature controller knows what temp it is in the room. Often in commercial steam rooms clients tend to spray cold water on the sensor which causes damage and alters the ohm rating to the point where the sensor is relaying incorrect room temps to the controller, causing high or low temperatures. Normally when the room is hot, it causes the alloy metal of the sensor to be hot. When cold water is sprayed on it, it immediately bring down the temp of the alloy and the thermal shock warps the metal causing the resistance values to change. Set your multi-meter to ohms and remove the sensor wires from the back of the controller. You will do your ohm reading on the sensor wires. Check the actual room temperature with a thermometer. At room temp 77 degrees you should be getting 10,000 ohms, at 100 degrees you should get 5827 ohms, and at 120 degrees you should get 3759 ohms. Note as the temp goes up the ohms go down, this should help you determine if your sensor is good. The other possibility is your steam solenoid valve is stuck in the open position. Simply check if there is voltage running to the solenoid. If there is no voltage but the room is filling with steam your solenoid is stuck open and needs to be replaced. The last is the controller, and by process of elimination if the sensor and steam solenoid are good then the controller may be the issue.